Description

A while back I released a video of a transforming birthday cake my wife and I made for our son. https://youtu.be/jtvTV-FrupU Amazingly the video went viral and since then I have been regularly asked by eager makers how to make one of their own.

So I started this project to feedback all the lessons learnt from the video version and bring you an easier project that you can build at home for your kids... both little and big.

Project Logs

I'm thrilled to announce that project member Anna from Scotland is the first to tackle this project. It was a struggle at times for Anna and her husband but they persevered and create a fabulous cake for their friends son.

Anna has provided heaps of feedback which I have used to improve the project information for all to come.

The first run of the printing is done and I'm really happy with the proportions and the standing motions some of parts aren't playing as well together.

In my experience with 3D modelling and printing this is to be expected. 3D modeling is great for designing the parts but as for interactions, how parts move with each other, there is little substitute for the real thing. So I have a few refinements to make, mostly on how the arms open and shut and how the head is raised and lowered.

In the picture you can see the little lead and steel weights I am using as stand-ins for the cake to make sure the motor and batteries are up the the task.

Also pictured is the switch (top-left corner) that I am using to activate the open and down motion for testing. Currently it is a simple switch, no Arduino yet. I am using 6AA batteries for about 8v of power and so far this seems to be enough juice to lift the frame with 900 grams of weight in 6 seconds.

I have started 3D printing and so far, so good. There are are many pieces to print so whilst that is happening I have started on the actuation design. Using a gearmotor, leadscrew (m4 thread rod) and micro switched for end-stops.

This week I received my Laser cut base from Ponoko. I think Ponoko will be my go-to online shop for Laser cut from now on. I was really chuffed with their service: functional and easy to use web site app, automated price quotes and fast turn around time. Plus $20 off my first order.. niiice.

The only trade off for this efficiency is that they use set sheet/template sizes so I had to shrink the bases design a little too get it to fit in the most affordable template.

A little bit of masking tape and wood glue and the base is now complete.

I'm excited to get started printing but to avoid wasting time or filament I started with a test print (see montage pic), because there are moving parts it's important to get the fit right.

I'm printing on a lulzbot mini using default medium speed settings profile. I'm aware not all 3D printers are as good as the Mini so I am making the gaps between pin and barrel wider than I normal do. Additionally all the holes sizes are common metric drill bit sides (namely 2.5, 6 and 10mm) so if your printer gets over excited you can just drill the hole to clean them up.

In the original cake I used M3 bolts which are more at home in metal than plastic. This time I am using common hardware wood screws. Only two types: 25mm to securely join the feet to the base and 9mm everywhere else.

The tests print gave me the feedback I need so I can now start printing and begin the print-fail-feedback-repeat cycle until I am happy with the 3D models, then I will publish the stl's here on hackaday.

Recently I have been preparing the body parts for printing and assembly. Adding tolerances (gaps between parts) , beveling (removing square edges for cleaner prints) and adding little pegs with holes so the whole thing can be assembled with the same sized small screws.

I'm just waiting on some red and blue PLA filament to arrive to print some test parts and check all my guesses.

As we are creating something that will interact with food we need to be food safe. PLA is considered food safe (It's made from corn starch) and we will use food-safe petrolium jelly as a lubricant in all the joints.

Where the original cake had 2 motors, the new cake will have only one.

This time instead of an expensive stepper motor I want to use a DC motor with a leadscrew (pictured below) because they are cheap ($5 from Ebay) and the control electronics, a DC motor controller shield, is also affordably prices on eBay.

The Cake, including icing, will weight an estimated 1.6kg (3.5lbs). But because of the leverage of the lifting arm the motor will have to move 3x that, 4.8kg (10.5lbs)

I hope to use no more than 6 AA batteries to power the electronic but there is a bit of trial and error to come after my parts arrive in a few weeks.

Naturally I will create a BOM (Bill of Materials) as the project progresses which will include a list of all the final electronics and links of where to buy them.

Hi Russel. I was wondering - some elements are needed to be printed once (like the "chest" or head plate, as well this U shaped element that connects to the motor...What about rest of elements? I'm trying to figure it out from this coloured drawing you uploaded, but seems my 3D imagination is not that great. I'm especially stuck with hinges and chassis elements... 2x both shin and foot, 2 arms and arm hinges, 2 shin platforms...but do I need 4x connection rods?I'd appreciate every help! Thanks!Anna

Yes you can make it out of plywood if you like but make sure to get the edges of the mounting rectangle "holes" nice and smooth. The 3d printed leavers might catch there and cause you trouble. I have uploaded a template for https://www.ponoko.com/, I recommend using them, they are great and it will save you a bunch of time and hassle.

Hi JahFyahh, thanks for getting in contact and reminding me to do this, I have uploaded the STL files. If you run into any issues or need more information just let me know.They are for a 3D printer with a 6" build plate, what size printer do you have?

Hi JayFyahh I just create a new zip file with all the full size STL files. NOTE that you will have to print the mirror side of the legs and arms. I will soon create a diagram explaining how the pieces come together.

Hi Russell, love the project and i would like to build it for my son. His birthday is coming up this june, will you upload the 3D files soon? I would be happy with the old files so I can build from there.